Track circuit apparatus



July 22, 1941.

H. A. TH OMPSON TRACK CIRCUIT APPARATUS .Filed Sept. 30, 1939 INVENTOR[HS ATTORNEY Patented July 22, 1941 'irtACK CIRCUIT APPARATUS Howard A.Thompson, Edgcwood, Pa., assignor to The Union Switch & Signal Company,Swissvale, Pa., a corporation of Pennsylvania Application September so,1939, Serial No. 297,389

7 Claims.

My invention relates to track circuit apparatus and more specifically toapparatus of this character which provides protection against falseenergizationof a track relay due to failure of the insulated rail jointswhich serve to insulate ad joining track circuits. I

One object of my invention is to incorporate the protective featuresinto the rail joints themselves by passing current through the railjoints in a novel manner. Another object is to elimi nate the necessityfor using polarized or twoposition track relays and staggering thepolarity of adjoining track circuits to avoid false relay operation. Afurther object is to provide apparatus which will be simple, safe, andreliable in its operation. Other objects and advantages will becomeclear as the description progresses.

I shall describe several forms of apparatus embodying my invention and.shall then point out the novel features thereof in claims.

In the accompanying drawing, Fig. 1 is 21. diagrammatic view showing oneform of apparatus embodying my invention. Figs. 2, 3 and 4 arediagrammatic views showing modified forms of the apparatus shown in Fig.1, and also embodying my invention.

Similar reference characters refer to similar parts in each of theseveral views.

In railway signaling track circuits, provision must be made againstfalse energization of the track relays due to leakage of current fromadjoining track circuits over rail joints in which the insulation hasbeen broken down. In general, this false energization can be preventedby using polarized or two-element track relays and staggering thepolarity in adjoining track circuits so that the leakage current willcause a reversal or deenergization of the track relay. In alternatingcurrent track circuits, the use of twoelement track relays sometimespresents a problem due to the fact that when the transmission line issectionalized, one element, of the track relay at the secticnalizinglocation may receive current from one source of supply while the otherelement receives its energy from a different source, thus rendering therelay inoperative. Accordingly, difliculties are encountered withtwo-element alternating current relays where sectionalizing must beemployed.

The apparatus embodying my invention does propulsion territory. Theinsulated rail joints which I employ may be of the usual type exceptthat the method of making the track circuit connections is changed. Inthe event that the insulation breaks down, it. is not only impossiblefor track circuit energy to feed around the defective joint into theadjoining track circuit, but the failure will also be indicated by thedeenergi zation of the track relay in the track circuit wherein thefailure has occurred.

This protection is obtained by arranging the electrical connections totheinsulated joint in such a manner that if the insulation between onerail and theangle bars which supports the rail is broken down, one halfof the-impedance bond which is connected to that rail will beshort-circuited, thereby effectively short-circuiting the track circuit.t will be apparent, therefore, that my invention permits the use ofsingle element alternating current track relays (or single elementdirectc'urrent track relays energized from a transformer and rectifiercombination) thus eliminating the transmission line sectionalizing 1 neras those shown at location D. Each track relay TR is energized from itsassociated track transformer T over the rails and a suitable currentlimiting reactor X, in the usual-manner. Each track transformer isenergized from a suitable source of alternating current having theterminals BXCX. The impedance bonds IB are connected across the rails atthe two ends of each track circuit for the usual purpose of permittingthe flow of propulsion current over the two rails in parallel, withoutinterferingwith the operation of the alternating current track circuits.

I shall now describe the manner in which the electrical connections aremade at the insulated rail joints to provide protection in the eventthat the insulation breaks down. Looking at the rail joints A and B atlocation D, the reference characters 2, 2a designate the angle barswhichserve toclamp the two rail ends together through the rail jointinsulation 3, 3a, and the reference character 4 designates theinsulating end post between the two rail ends. For simplicity, I havenot shown the clamping bolts in the diagram but it will be understoodthat the usual arrangement of bolts which are insulated from the anglebars is used.

Propulsion current flowing in rails I and Ia of section CD will flowthrough the two halves of the impedance bond IE to its mid-point. Fromthis mid-point, the path of the current may be traced through wire 5,angle bar 2a,, wire 6, angle bar 2, wire I, angle bar 2a, wire 8, anglebar 2, and wire 9, to the mid-tap of the impedance bond IB and the tworails of section DE. Should any of the connections in this path becomebroken, the propulsion current will be interrupted (in the case of asingle track road where cross-bonding is not present to provide analternate path for the propulsion current) and the train will fail toreceive propulsion energy as it passes from one to the other section sothat this condition will be readily detected. On a multiple track road,visual inspection may be used. If, on the other hand, the insulation 3or 3a between the upper rail I and the angle bars 2 and 2a should fail,then the upperhalf of the impedance bond 13 immediately to the left ofthe faulty rail joint will become short-circuited, as will be obviousfrom the drawing, so that the track circuit voltage between the rails Iand, la will be reduced to practically zero whereupon the track relay TRat location C will release. Likewise, if the insulation 3 or 3a betweenthe lower rail Ia and the angle bars 2 and 2a should fail, the lowerhalf of the impedance bond IE will be short-circuited, with the sameresult.

If the insulation between the rail I of section D-E and either of theangle bars 2 and 2a should fail, a'short-circuit will be placed on theupper half of the impedance bond 1'B immediately to: the right of therail joint so that the track circuit voltage in section D-E will bereduced to practically zero and the associated track relay TR willaccordingly release. Similarly, a failure of the insulation between therail Ia of section D-E and either of the angle bars will cause ashort-circuit to be placed on the lower half of the 7 bond lIB, causingrelay TR to release.

It will be apparent from the foregoing that the apparatus provideseffective protection in a simple and direct manner against any failureof an insulated rail joint in an alternating current track circuit suchas might endanger traffic passing through the section; It will also benoted that the ordinary type of insulated rail joint may be used in thisapparatus, the chief difference being in the manner of makingconnections to the various parts of the rail joint. In the event thatthe rail joint breaks down, it is not only impossible for track circuitenergy to be fed around the rail joint into the adjoining track circuit,which precaution is ordinarily considered sufiicient from the standpointof protection to traffic, but the fault will also be indicated by arelease of the track relay in the associated track circuit.

The nature of the protection which the apparatus provides is such thatit is not essential to use two-element or polarized track relays for thepurpose of obtaining the necessary brokendown rail joint protectionbecause the failure will be detected by a single-element type of'trackrelay. Accordingly,--the transmission line sectionalizing problem nolonger offers anydifficulty. In} the case of a propulsion road, theimpedance bonds IE will already be present in the track cirof theinsulated rail joints will be required. In steam road territory,however, it will ordinarily be necessary to provide auxiliary impedancebonds but in this case, these may be nothing more than small reactorcoils. On account of the absence of propulsion current, the connectionsto the angle bars and to the auxiliary impedance bonds will not bechecked automatically in the latter case. However, this condition is notvery serious because the nature of these connections is such that theycan readily be checked by visual inspection as aften as conditionsrequire. If an automatic check is desired, then the apparatus of Fig. 2can be used to provide the required indication.

Referring now to Fig 2, the insulated rail joints A and B are showndiagrammatically in this figure, for simplicity, but it will beunderstood that the construction of these joints and the electricalconnections thereto are identical with those previously described forthe rail joints A and B of Fig. 1. In order to check the continuity ofthe circuit through the rail joints, I have provided a checkingtransformer CT which furnishes a small checking current sufficient tomaintain the checking relay CR energized. The track transformer TI andthe track relay TRI each have a mid-tap in the track-connected windingthrough which the checking current is caused to flow. This current willnot cause any appreciable change in the flux condition of either devicesince the direction of the checking current is opposite in the twohalves of the winding of each device. The current limiting reactor XI ispreferably connected in series with the input rather than the outputwinding of the transformer TI in order not to cause too much unbalancein the checking current in the two rail paths which this current takes.

As will be obvious from the drawing, the checking current from theoutput winding of the transformer CT flows through the Winding of relayCR and divides in the winding of relay TRI so that one portion flowsover rail I and the other portion flows over rail la. The checkingcurrent then unites in the right-hand bond IBI and flows over the railjoint connections 9, l0 and I I whereupon it again divides as it flowsthrough the lefthand impedance bond IBI and over the rails I and la, tounite again as it leaves the mid-point of the output winding oftransformer TI and returns to the checking transformer CT.

Should any connection become broken in the checking circuit tracedabove, relay CR will re- Referring to Fig. 3, the apparatus of thisfigure shows an alternative arrangement similar to that 7 shown in Fig.2 for steam road territory, but dispensing with the checking transformerand its associated checking relay. It will be understood that theinsulated rail joints A and B of Fig. 3 are constructed in the samemanner as shown in Fig. 1 but the connections to these joints aresomewhat different. The apparatus is so arranged that the rail jointsA'and B arechecked both as to insulation failure as well as breakage ofthe connections. The track transformer T2 has a mid-tap in its outputwinding, as in Fig. 2, but instead of a single track relay, two relaysTRZa and TR2b are employed, of which relay TRZa is intended to performthe usual signal control functions. The apparatus operates as follows:

When the rail joints A and B are both intact, track circuit current fromthe track transformer T2 associated with relays TR2a and TRZb will flowover a circuit which may be traced fromthe upper rail I, through wire[5, winding 15 of the auxiliary transformer ATa, wire l1, angle bar 2a,wire 3, angle bar 2, wires I9 and 20, angle bar 2a, wire 2|, angle bar2, wire 22, winding 23 of the auxiliary transformer ATb, and wire 24, tothe lower rail I a. Accordingly, both transformers ATa and ATb will beenergized so that relays TRZa and 113217 will also be energized throughthe associated rectifiers Ra and Rb. The auxiliary track relay TRZbcontrols the energization of the main track relay TR2a over its frontcontact 25 and an obvious circuit.

If the insulation should break down at the right-hand half of the railjoint A between the rail I and either angle bar 2 or 2a, then winding l6of the transformer ATa will be short-circuited so that relay TRZa willrelease. A breakdown of the insulation at the right-hand half of railjoint B, between the rail Ia and either anglebar 2 or 2a will similarlycause winding 23 of the transformer ATb to become short-circuited, thusreleasing relay TRZb and causing relay TR2a to release, in turn, due tothe opening of the front contact 25. Should the insulation break downbetween the rail I and either angle barat the left-hand half of the railjoint A, then portion 26 of the output winding of the track transformerwill be short-circuited so that the track circuit to the left of thefaulty rail joint will be substantially deenergized. Likewise, a failurein the insulation between the rail Ia and either angle bar at theleft-hand half of the rail joint A track transformer winding, againdeenergizing the track circuit to the left of the rail joint.

It will be clear, therefore, that the apparatus of Fig. 3 providespractically complete protection against any failure at the rail joint.The only connection which is not automatically checked in Fig. Bis thewire 28 which can, of course, be so arranged and connected as to makemechanical breakage thereof very unlikely and render visual inspectionof the connection comparatively easy.

In Fig. 4, I have shown a modification of the apparatus of Fig, 3 inwhich the two track relays are replaced by a single track relay TR2controlled from a single auxiliary transformer AT through a rectifier R.The energizing circuit for windings I6 and 23 of the transformer AT isidentical with that traced for the corresponding windings in Fig. 3. Thewindings l6 and 23 are so connected as to aid one another in energizingthe rectifier R and relay TRZ. Should a failure develop at theright-hand half of either rail joint A or B, the associated winding I 5or 23 will be short-circuited, so that relay TRZ will release.Similarly, a failure at the left-hand half of either rail joint willshort-circuit the respective portion 26 or 21 of the track transformerwinding. The protection provided by the apparatus of either of Figs. 3or 4 is, accordingly, substantially the same.

The apparatus described in the foregoing figures is not intended toprovide protection against a failure involving a breakdown of theinsulation at an end post such as 4 in Fig. 1. In actual practice, ithas been found that a failure of an insulated rail joint over its endpost is quite uncommon. It should also be noted that when the ordinarytype of insulated rail joint protection is used, two failures mustordinarily occur before a connection is established between theadjoining rails and the protective apparatus is brought into play. Thatis, the insulation must fail between one angle bar and a rail and alsobetween th same angle bar and the other rail. In the apparatus embodyingmy invention, however, a single failur of the insulation between 'anangle bar and a rail constitutes a broken-down rail joint and isdetected by the apparatus. The result may be to accelerate thereplacement of defectiv rail joints, but this will ordinarily becompensated for by an earlier discovery of a defect in the joint and anincrease in the safety factor. As a rule, it has been found that whenone portion of the rail joint breaks down, the remaining portions areabout ready to give way also, so that prompt detection of the firstfailure is desirable.

Although I hav herein shown and described only a few forms of trackcircuit apparatus embodying my invention, it is understood that variouschanges and modifications may be made therein within the scope of theappended claims withoutdeparting from the spirit and scope of myinvention.

Having thus described my invention, what I claim is:

1. In combination, a stretch of railway track divided intoadjoiningtrack sections by means of an insulated rail joint in each rail of saidtrack, each said insulated rail joint comprising a conducting bar oneach side of the rail separated therefrom by insulation, a tracktransformer for one of said sections having a midtap in itstrack-connected winding, 21. first and a second detection relay for anadjoining track section, means for energizing said two detection relaysfrom the rails of said adjoining section over a circuit which includessaid conducting bars and the input windings of two transformers, one foreach relay, all connected in series, and a connection from said mid-tapto said conducting bars, whereby a breakdown of the insulation between aconducting bar and a' rail of said one section will short-circuit onehalf of said track transformer winding and whereby a breakdown of theinsulation between a conducting bar and a rail of said adjoining sectionwill short-circuit one of said input windings to thereby cause theassociated detection relay to release.

2. In combination, a stretch of railway track divided into adjoiningtrack sections by means of an insulated rail joint in each rail of saidtrack, each said insulated rail joint comprising a conducting bar oneach side of the rail separated therefrom by insulation, means forelectrically connecting said conducting bars with one another, a tracktransformer connected across the rails of one of said sections forenergizing the usual track circuit apparatus and having a mid-tap in itstrack-connected winding, and an electrical connection from said mid-tapto said conducting bars, whereby a breakdown of the insulation between aconducting bar and a rail of said one section will short-circuitone-half of said track transformer winding to thereby cause substantialdeenergization of said track circuit apparatus. a V

3. In combination, a stretch of railway track divided into adjoiningtrack sections by means of an insulated rail joint in each rail of saidtrack, each said insulated rail joint comprising a-conducting bar oneach side of the rail separated therefrom by insulation, a detectionrelay for each of said rail joints, means for energizing one of saiddetection relays from the rails of one of said sections over a circuitwhich includes said conducting bars in series, and means including acontact of said one detection relay for also energizing the otherdetection relay from the rails of said one section over said circuit,whereby a defect in said circuit will cause both of said relays torelease.

4. In combination, a stretch of railway track divided into adjoiningtrack sections by means of an insulated rail joint in each rail of saidtrack, each said insulated rail joint comprising a conducting bar oneach side of the rail separated therefrom by insulation, means forelectrically connecting said conducting bars with one another in series,and a detection relay energized from across the rails of one of saidsections over a circuit which includes said conducting bars and theelectrical connections therebetween as well as the input winding of atransformer all in series, said input winding comprising two aidingportions, one terminal of each of said portions being connectedrespectively with one and the other rail of said one section, and

the remaining terminal of each of said portions being connectedrespectively with the first and mid-tap and said conducting bars, and adetection relay energized from across the rails of an adjoining sectionover a circuit which includes said conducting bars and the electricalconnections therebetween as well as the input winding of a transformerall in series, said input winding comprising two aiding portions, oneterminal of each of said portions being connected respectively with oneand the other rail of said adjoining section, and the remaining terminalof each of said portions being connected respectively with the first andfourth of said conducting bars in said series arrangement thereof.

6. In combination, a stretch of railway track divided into adjoiningtrack sections by means of an insulated rail joint in each rail of saidtrack, each said insulated rail joint comprising a conducting bar oneach side of the rail separated therefrom by insulation, means forelectrically connecting said conducting bars with one another in series,a track transformer for one of said sections having a mid-tap in itstrack-connected winding, a track relay for an adjoining sectionenergized by a transformer having a track-connected input windingcomprising two aiding portions, an electrical connection between saidmid-tap and said conducting bars, and means for connecting the remainingterminals of said portions of the transformer input winding respectivelywith the first and fourth of said conducting bars in said seriesarrangement thereof.

7 In combination, a stretch of railway track divided into adjoiningtrack sections by means of an insulated rail joint in each rail of saidtrack, each said insulated rail joint comprising a conducting bar oneach side of the rail separated therefrom by insulation, a detectionrelay for each of said rail joints, and means for energizing said twodetection relays from therails of one of said sections over a circuitwhich includes said conducting bars and the input windings of twotransformers, one for each relay, all connected in series, whereby abreakdown of the insulation between a conducting bar and a rail of saidone section will cause the input winding of one of said transformers tobecome shortcircuited to thereby release the associated detection relayand whereby a defect in said circuit will cause both detection relays torelease.

' HOWARD A. THOMPSON.

